The report, released ahead of the councillors’ debate next Thursday, called the development “excessive” and stated the design had failed to achieve the world class architectural response required for the site in the heart of Edinburgh.

“The resulting harm caused by the proposed extensions significantly outweighs the economic benefit and benefit of bringing the building back into long-term use,” they said.

Councillors have been urged to knock back the hotel proposals. Picture: Contributed

Planners also slammed the impact the proposal would have on the setting.

“The development will damage the unique views of this highly visible and highly sensitive site by introducing an additional quantum of development on a hillside of unique individual structures, damaging the composition of the buildings, monuments and the landscape.

“The benefits to the City’s economy and to tourism through bringing an ‘at risk’ building back into a sustainable long-term use are not outweighed by the very significant harm to the built heritage and landscape of the city.”

The idea of turning the building into a hotel won a council-run design contest in 2010, but the final plans sparked anger when it emerged they involved multi-storey extensions. Councillors rejected the initial plans in 2015 but a revised proposal was submitted, reducing the number of hotel rooms from 147 to 127 and lowering the extensions.

David Orr, chairman of Urbanist Hotels, one of the firms behind the hotel scheme, said the recommendation threatens the future of the site.

“We need to be very clear about what is now at stake for the very future of the Old Royal High School,” he said.